One problem that can be annoying, inconvenient, and sometimes dangerous to those who depend upon motor vehicles is having the motor vehicle battery become discharged by leaving the lights on after stopping the engine and departing the vehicle. This problem is most likely to occur when driving under conditions when lights are necessary for at least some portion of the trip except at the destination, as for example when beginning a trip before dawn and arriving after the sun has risen, or as a result of variable weather conditions.
In order to prevent this problem, some vehicles are equipped with buzzers that are activated if the headlights are on, the key is removed from the ignition, and the vehicle door is opened. Other vehicles, particularly older vehicles, have no such warning system.
One problem with prior art systems is that they must be built into the existing vehicle electrical system, which can create difficulties for the average consumer. Another problem with prior art systems that rely upon switch contacts--for example door switches--for operation is that the switch contacts can become dirty or corroded so that the system fails to function properly, thereby leaving the driver with a false sense of security that the vehicle battery will not become discharged by inadvertently leaving the lights on. Yet another problem with some prior art systems is that they incorporate energy dissipating circuit elements in series with the vehicle lighting system, and accordingly are a source of energy loss which causes reduced fuel economy and reliability. Yet another problem with some prior art systems is that the warning device is continuously activated as long as the problem is present, without any provision for deactivating the warning system, which can be annoying to drivers, particularly if they intentionally wish to have the lights on.
U.S. Pat. No. 5,041,761 teaches a coil in series with a lamp circuit and wound around a magnetically permeable core which has a gap within which is placed a magnetic flux sensor. When the lamp is on, a current in the coil creates a magnetic field in the magnetically permeable core that is sensed by the magnetic flux sensor, which switches an open collector transistor that drives an automotive circuit. One disadvantage of this invention, particularly for retrofit applications, is that the lamp circuit must be interrupted to insert the current sensor. Furthermore, this sensor is not responsive to whether or not the engine is running, nor does it provide any override or time-out features.
U.S. Pat. No. 4,104,613 teaches a vehicle headlight alarm comprising a relay coil in series with the current to the headlights and taillights, and a normally open associated relay switch in series with the current provided by the vehicle battery through the vehicle ignition switch--when in the OFF position--to an audible alarm. When the lights are on, the relay coil closes the associated relay switch, and if the ignition switch is off, the audible alarm is activated by the current provided by the vehicle battery through both the OFF-positioned ignition switch and the closed contacts of the associated relay switch. One disadvantage of this invention, particularly for retrofit applications, is that it requires modification of the existing electrical system. A relay coil must be inserted in the lamp circuit for headlight sensing, and an ignition switch with contacts which are open when ignition is on, and closed when ignition is turned off, is required for detecting the operative state of the engine. Furthermore, this invention is not responsive to whether the engine is actually running, and therefore generating power. Yet further, the circuitry added to the lighting circuit causes excessive power to be consumed when the lights are on. Yet further, there are no override or time-out features in the control of the warning device.
U.S. Pat. No. 4,058,793 teaches a vehicle headlight warning circuit that connects between the non-battery terminals of the vehicle headlight switch and the vehicle ignition switch that generates an audible warning if the headlights are turned on when the vehicle ignition switch is off. One disadvantage of this invention is that current is passed through the ignition circuit when the ignition is off if the headlights are on. Furthermore, this invention requires a conductive path to ground through the ignition system when the ignition system is off. Yet further, this invention does not provide any time-out control of the associated warning device.
U.S. Pat. No. 3,898,612 teaches a headlight warning system including a buzzer unit having a relay coil that is activated by either the ignition switch, or by the headlight switch through the associated normally closed relay coil contacts. If the ignition switch is turned off while the headlights are on, the relay coil is alternately activated and deactivated, causing the relay contacts to emit an audible warning signal. One disadvantage of this invention, particularly for retrofit applications, is that it requires modification of the existing electrical system. Furthermore, there is a continuous current through an associated relay coil when the ignition is on, which wastes power. Yet further, there are no override or time-out features in the control of the warning device.
U.S. Pat. No. 3,467,831 teaches a circuit breaker for vehicle lights incorporating at least one relay circuit in the vehicle electrical system for automatically shutting off the vehicle lights when a vehicle door is opened after the ignition has been turned off with the lights left on. One disadvantage of this invention is that it automatically shuts the lights off when the ignition is turned off, which may be contrary to the wishes of the driver. Furthermore, this invention would be relatively difficult to retrofit to an existing vehicle, and requires modification of the existing electrical system.
U.S. Pat. Nos. 2,942,235, 2,780,797, 2,756,408 teach other arrangements for systems to warn drivers when the headlights have been left on after the ignition has been turned off. Each of these systems incorporate relays integrated into the vehicle electrical system. Accordingly, one disadvantage of these inventions, particularly for retrofit applications, is that they require modification of the existing electrical system.
U.S. Pat. No. 4,539,520 teaches the use of a Hall effect sensor in combination with a magnetic flux collector to sense the current in an existing current carrying conductor that is part of an electrical power transmission system.